In wireless communications, wireless devices are now capable of sending or receiving communications with multiple carriers simultaneously. Devices use frequency synthesizers based on oscillators, such as voltage-controlled oscillators (VCOs) to generate each of the desired frequencies. Depending on the target frequency bands, a device may be required to generate multiple, similar frequencies simultaneously.
When two VCOs run at similar frequencies however, VCO pulling occurs, which causes phase noise degradation and in-band spurs. VCO pulling can cause the output frequencies of the VCOs to vary from the target frequency.
VCO pulling is currently avoided by operating multiple VCOs at non-similar frequencies even if target frequencies for local oscillators (LOs) are similar. For example, if the wireless device requires two LO frequencies of 2.4 and 2.5 GHz, respectively, implementation of the frequency plan would have one VCO producing an operating frequency of 2.4 GHz, while the second VCO produces a frequency of 10 GHz that is sent through a divide-by-4 circuit to produce the LO frequency of 2.5 GHz. Such implementation leads to high current consumption. Use of such high frequencies also exasperates issues relating to the use of VCOs, such as phase noise degradation and in-band spurs.
In view of the foregoing, it would be desirable to run multiple VCOs to generate similar frequencies. In particular, it would be desirable to enable VCOs to effectively operate in a narrow range of operating frequencies for a receiver on the wireless device.